How to pass variables between applications?

I am able to send fixed string from InDesign to Bridge like in my "sample 1", but not able to send variable like in "sample 2" (myDocName is the variable). How to solve this?

// sample 1
var bt = new BridgeTalk;
bt.target = "bridge";
bt.body = "var mydoc = 'MacintoshHD/MyFolder/Bot02.indt'; app.document.thumbnail = new Thumbnail(File(mydoc));"
bt.send();

// sample 2
var bt = new BridgeTalk;
bt.target = "bridge";
var myDocname = "MacintoshHD/MyFolder/Bot02.indt"
bt.body = "var mydoc = myDocname; app.document.thumbnail = new Thumbnail(File(myDocname));"
bt.send();

regards

Erkki